In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions of the resist film become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a shorter wavelength (higher energy) than these excimer lasers, such as extreme ultraviolet radiation (EUV), electron beam (EB), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material satisfying these requirements, a chemically amplified resist composition which contains a base component of which the solubility in a developing solution changes by the action of acid and an acid-generator component which generates an acid upon exposure is used in the related art. For example, when the above developing solution is an alkali developing solution (alkali developing process), as a chemically amplified positive resist composition, a resist composition containing a resin component (base resin) of which the solubility in the alkali developing solution increases by the action of acid and an acid-generator component is generally used. If a resist film formed of such a resist composition is selectively exposed for forming a resist pattern, an acid is generated by the acid-generator component in the exposed portion, and the solubility of the base resin in the alkali developing solution increases by the action of acid, whereby the exposed portion becomes soluble in the alkali developing solution. Accordingly, by performing alkali developing, the unexposed portions remain as a pattern, resulting in the formation of a positive-type pattern.
The base resin used exhibits increased polarity under the action of acid, thereby exhibiting increased solubility in an alkali developing solution, whereas the solubility in an organic solvent is decreased. Accordingly, if a solvent developing process that uses a developing solution containing an organic solvent (an organic developing solution) is employed instead of an alkali developing process, then within the exposed portions of the resist film, the solubility in the organic developing solution decreases relatively, meaning that during the solvent developing process, the unexposed portions of the resist film are dissolved in the organic developing solution and removed, whereas the exposed portions remain as a pattern, resulting in the formation of a negative-type resist pattern. This type of solvent developing process that results in the formation of a negative-type resist pattern is also referred to as a negative tone development process (for example, see Patent Document 1).
Currently, as the base resin of the chemically amplified resist composition used for ArF excimer laser lithography or the like, an acrylic resin or the like that contains structural units derived from (meth)acrylate esters within the main chain is generally used since this resin exhibits excellent transparency around 193 nm (for example, see Patent Document 2). Here, the term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position. The term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position.
In recent years, as the base resin, a resin having an acid-generating group which generates an acid upon exposure has been proposed. For example, a resin component containing an acid-generating group which generates an acid upon exposure and an acid-decomposable group which exhibits changed polarity by the action of acid in the structure has been proposed (for example, see Patent Documents 3 to 5). The resin component functions not only as an acid generator but also as a base component, and enables a chemically amplified resist composition to be constituted only with a single component. In other words, when this type of resin component is subjected to exposure, acid is generated from the acid-generating group within the structure, and the action of that acid causes decomposition of the acid-decomposable group, thereby forming a polar group such as a carboxyl group that causes an increase in the polarity. Accordingly, when a resin film (resist film) formed of the resin component is selectively exposed, the polarity of the exposed portion increases. Therefore, if developing is performed using an alkali developing solution, the exposed portion is dissolved and removed, whereby a positive resist pattern is formed.
As resist patterns are increasingly miniaturized, for the resist materials, further improvement is required not only in sensitivity or resolution but also in various lithography properties such as exposure latitude, mask reproducibility, and a pattern shape (roughness, rectangularity of a cross-sectional shape, and the like). For example, roughness on the side wall surfaces of a pattern can cause various defects such as non-uniformity of the line width of line and space patterns, or distortions around the holes in hole patterns. There is a concern that shape defects of a resist pattern may negatively affect the formation of a fine semiconductor element, and the like. Consequently, as the pattern becomes finer, improving the shape defects becomes more important.
Regarding such requirements, for example, Patent Documents 6 to 8 propose using a polymeric compound containing plural kinds of acid-decomposable groups as a base resin so as to improve the lithography properties and the pattern shape.